Capping machines for the application of prethreaded closures onto prethreaded containers have been known for years. In order to insure that a prethreaded closure is not applied too tightly, which could possibly result in damage, conventional screwcapping machines are provided with a screwcapping head having a torque-dependent clutch. The clutch limits the maximum torque which can be transmitted to the prethreaded closure. In the past, slipping clutches and mechanical torque limiting clutches have been used. However, magnetic clutches have replaced some of these clutches in certain applications as is disclosed in U.S. Pat. Nos. 4,364,218 and 4,492,068 and 4,599,846. One of the disadvantages of using one of the above-identified magnetic clutches is that the magnets create a reverse torque once a predetermined torque value is reached. In short, the screwcapping head oscillates once the closure is tightened onto a container until the screwcapping head is lifted away from the container. This inherent torque reversal feature tends to reduce the efficiency of such screwcapping heads.
A new type of magnetic clutch, called a hysteresis clutch, has recently been developed which uses a permanent magnet in conjunction with a hysteresis magnetic material. The use of a hysteresis clutch is disclosed in U.S. Pat. No. 4,485,609 and in the April, 1982 issue of Popular Mechanics on page 96, in an article entitled "How Magnets and Sonar Make Anyone an Expert Fisherman" by Stan Fagerstrom. In U.S. Pat. No. 4,485,609, a ring of magnetic material encompasses a ring of a hysterloy magnetic material, and the torque of the clutch is varied by axially displacing one member relative to the other. One drawback of this design is that the heavy magnetic material and the hysterloy are located distally away from the longitudinal centerline of the screwcapping head. Such a design creates a large inertia which makes it hard to stop the rotation of the screwcapping head, especially at higher speeds. Likewise, the magnets and inductant rotor, used in the clutch described in Popular Mechanics, are arranged parallel to and distally away from the central longitudinal axis of the fishing reel. This design also creates a large inertia value which is detrimental when used in a screwcapping head.
Now a screwcapping head has been invented which uses a hysteresis clutch which improves upon the prior art.